Methods and compositions for the generation of peracetic acid on site at the point-of-use

ABSTRACT

Methods for the generation of non-equilibrium solutions of peroxyacetic acid are disclosed. These methods comprise introducing triacetin sad aqueous hydrogen peroxide to water, mixing, and then adding an aqueous source of an alkali metal or earth alkali metal hydroxide. Triacetin is converted rapidly and with a high conversion rate into peracetic acid. These methods produce solutions with a high level of peracetic acid.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a divisional application of co-pending U.S. patent applicationSer. No. 14/019,296 filed on Sep. 5, 2013, which is a divisional ofprior application Ser. No. 13/065,553 filed on Mar. 24, 2011, now U.S.Pat. No. 8,546,449 issued on Oct. 1, 2013, pursuant to 35 U.S.C. §§120and 121, and hereby incorporates both applications by reference in theirentirety.

FIELD OF INVENTION

The invention relates to liquid compositions and methods of using theliquid compositions for the generation of a peroxyacetic acid sanitizeron site in proximity to the point-of-use. The invention also relates toa solid bleaching and stain removal composition.

A. Liquid PAA Disinfectants and Sanitizers

This is a divisional of prior application Ser. No. 14/019,296 filed onSep. 5, 2013. Disinfectants and sanitizers based on peroxyacetic acid(PAA), also commonly known as peracetic acid, are used in the dairy,food and beverage processing industries for clean-in-place pipeline andequipment disinfecting and cleaning, for fruit and vegetable washing,and in the treatment of meat, poultry and seafood products. Peroxyaceticacid disinfectants are also used in the treatment of cooling water,process water, and municipal wastewater. Other uses include slime andbiofilm removal in papermaking processes.

Peroxyacetic acid products are supplied as stable equilibrium ternaryaqueous solutions of peroxyacetic acid, acetic acid, and hydrogenperoxide. They are prepared in advance of delivery, typically byreacting hydrogen peroxide with acetic acid in the presence of a mineralacid catalyst. Although some PAA is formed immediately, the PAA does notreach its maximum concentration until after several days. A metalchelating agent, such as hydroxyethylidene diphosphonic acid (HEDP) ordipicolinic acid, is also introduced to suppress the transition metalcation catalyzed decomposition of peroxygen compounds. The PAA productis then placed in containers, such as totes, drums and pads, inpreparation for shipment to the end user. Typical commercial productshave concentrations of PAA of about 1-15% w/w, although a concentrationof up to 30% is possible. However, the latter concentration product onlyfinds captive use because of its extremely hazardous and explosiveproperties.

There are several problems with the use of equilibrium solutions of PAA.First, the low concentration of PAA (1-15%) means that most of theweight (85-99%) of the products consist of substantial amounts of inertingredients, such as water, acetic acid, and hydrogen peroxide. Thisresults in the need for larger product storage areas and causesincreased transportation and handling costs. Second, the products areinefficient in the use of both hydrogen peroxide (hydrogen peroxide) andacetic acid (AA). To maintain adequate storage stability of the PAA,either hydrogen peroxide or AA must be present at a level on a weightpercentage basis that is greater than the level of PAA, which increasesraw material costs. Third, the presence of the HEDP or dipicolinic acidstabilizer limits the amount of PAA that can be applied to certainfoodstuffs because the amount of HEDP or dipicolinic acid is regulatedby the Food acid Drug Administration (FDA). Fourth, the reaction betweenhydrogen peroxide and AA is quite slow in some cases, and typicallyrequires several days' time before the PAA product can be tested forquality confirmation. Therefore, manufacturers of these products muststore large inventories of the PAA product before it can be shipped tothe end user. Fifth, for transportation purposes, equilibrium solutionsthat are greater than 6% PAA are considered to be dangerous products andmust be labeled with the DOT marking “Organic Peroxide”, Hazard Class5.2, 8 (oxidizer, corrosive). If producers and end-users exceed theyearly threshold amount of just 6,666 lbs. of 15% PAA, they must fileRisk Management Plans with both federal EPA and state Authorities. Thisis an arduous and time-consuming process. In addition, producers ofequilibrium solutions of PAA that are over 6% PAA must obtain permittingby the local fire department and pay an extra hazardous materialshipping fee when the product is shipped from their facility. On theother hand, there are much less stringent requirements for products thatcontain hydrogen peroxide, and all reporting, permitting and shippingrestrictions are lifted for products that contain less than 27% hydrogenperoxide.

As a result of these problems, there have been various attempts to makenon-equilibrium solutions of PAA on site, at the point-of-use. Forexample, U.S. Pat. No. 7,012,154 discloses a system in which AA,hydrogen peroxide, water, and sulfuric acid are fed to a jacketedreactor for the production of PAA. A wiped-film distillation columnattached to the reactor condenses and isolates the pure PAA from the gasphase and immediately introduces it to the receiving water. This systemsuffers from a number of drawbacks. First, it is extremely capitalintensive due to the high cost of the equipment, including the reactor,heater, pumps, distillation column, and computerized control systemwhich ensures accurate metering of the reagents. Second, there aresignificant safety hazards associated with the production of pore PAAdue to its explosive properties. Third, the equipment and synthesisprocess is very complex and requires knowledgeable and highly trainedtechnicians to continuously operate and maintain the system in a safeand effective manner.

Other attempts to make non-equilibrium solutions of PAA at thepoint-of-use are based on electrolytic processes. U.S. Pat. No.6,171,551 and 6,387,236 disclose processes that employ a cell divided byan ion-exchange membrane in which PAA (and other oxidants includinghydrogen peroxide and ozone) are produced in the anode compartment whichconsists of an aqueous solution of acetic acid or acetate salt. Inaddition to the high costs of electricity and electrolysis equipment,these processes also result in a very low yield of PAA from the acetylprecursor. For example, the '551 patent reports that less than 14 ppm ofPAA was produced alter 90 minutes of electrolysis of a 490,000 ppmanolyte of aqueous potassium acetate. In addition, these processes aredifficult to perform intermittently.

Other methods of generating non-equilibrium solutions of PAA on site,using electrolysis, are described in WIPO International Publication Nos.WO 2004/0245116 and WO 2008/140988, and U.S. Patent ApplicationPublication No. 2009/0314652. These references disclose cationmembrane-divided electrolysis cells and the use of gas diffusionelectrodes to effect the cathodic reduction of oxygen gas to hydrogenperoxide under alkaline conditions. The hydrogen peroxide was thenallowed to react with acetic acid or an acetyl precursor to form PAA inthe bulk solution, whereupon the catholyte was directed to the acidicanode compartment of the cell to stabilize the PAA. This system suffersfrom several disadvantages. Due to the low solubility of oxygen in water(about 8 ppm maximum), the concentration of electroactive species isvery low, which forces the cell to operate at low current density(amperage per surface area of electrode). In order to produce ameaningful amount of hydrogen peroxide, the cells must have a very largesurface area. This requires high capital equipment costs and a verylarge footprint for the electrolysis equipment. Another disadvantage ofthis system is that it is very difficult to maintain steady-stateconditions and simultaneously balance the feed of acetic acid or acetylprecursor to the cathode compartment with the concurrent withdrawal ofacidified PAA solution from the anode compartment. This is becausecations carrying the cell current through the cation exchange membraneare always hydrated so as the cations move through the membrane, theyare accompanied by water molecules. As a result, the volume of theanolyte decreases and the volume of the catholyte increases, making thesteady-state condition difficult to maintain. It is difficult to performthis process intermittently. Finally, this system can only be ofeconomic value if the source of oxygen is air, which comprises 23%oxygen. However, the carbon dioxide contained in air causes carbonatesto precipitate, which Impedes the flow of electrical current, limitingor eliminating the production of hydrogen peroxide, and hence, PAA.

Another method of making a non-equilibrium solution of PAA at thepoint-of-use is disclosed in WIPO International Publication No. WO2008/140988 and U.S. Patent Application Publication Nos. 2009/0005590and 2007/0082832. These references disclose biosynthetic methods ofproducing peracids from carboxylic acids and carboxylic acid esters.These methods involve the use of perhydrolase enzymes to catalyze theperhydrolysis of the carboxylic acid or ester into the peracid using asolid or liquid source of hydrogen peroxide. Although these methods canproduce compositions containing up to 20 parts of peracid to one part ofhydrogen peroxide, they are limited by the amount of peracid that can beproduced before the perhydrolase enzyme is oxidized by the reactantproducts and ceases to function as intended. The highest concentrationof peracid disclosed by these references was 0.16% (1,600 mg/L).However, peracid or PAA solutions that are produced with enzymes havelimited appeal because they are very expensive to produce, and forregulatory reasons, the enzyme must be removed from the solution beforethe solution can be applied to food or hard surfaces for disinfectionpurposes. Removing the enzyme from the solution is not an easy task;thus, it is typically not done. Therefore, PAA solutions prepared byenzymatic methods are not suitable for the more broad commercial uses inthe food, dairy, beverage, meat, and poultry industries, which areregulated by the FDA and the Environmental Protection Agency (EPA).

Another method of generating non-equilibrium PAA at its point-of-userequires substituting the traditional mineral acid catalyst withsulfonic acid ion-exchange resins, as disclosed in U.S. Pat. No.5,122,538. A solution containing a 1.5:1 mole ratio of AA to hydrogenperoxide was passed through a column packed with a sulfonic acidion-exchange resin and produced a solution of 15% PAA within 30 minutes.The method described in the '538 patent suffers from the limitation thatit requires a large volume of expensive resin bed in order to beeffective. Moreover, all existing ion exchange resin systems are limitedby the fact the resin is subject to oxidative degradation by PAA andhave a short limited lifespan.

Other attempts to produce non-equilibrium PAA solutions on site, at thepoint-of-use, for bleaching cellulosic materials have reacted hydrogenperoxide with acetic anhydride. For example, U.S. Pat. No. 3,432,546discloses a process where hydrogen peroxide, acetic anhydride, and anammonium hydroxide catalyst were metered to a tubular reactor tocontinuously produce a solution containing 3.25% PAA with a conversionof 78% hydrogen peroxide. However, the process generated measurableamounts of diacetyl peroxide (0.44%) which is an explosion hazard.Moreover, the reaction product would be unsuited for any applicationother than cellulosic bleaching purposes because there was no attempt toremove the ammonium hydroxide catalyst from the reaction medium.Ammonium hydroxide is an undesirable contaminant in PAA products thatare used as disinfectants and sanitizers in the dairy, food, andbeverage processing industries, and in PAA products used in fruit andvegetable washing acid in the treatment of meat, poultry, and seafood.

Another process for generating non-equilibrium solutions of PAA on site,at the point-of-use was disclosed in U.S. Patent Application PublicationNo. 2009/0043132. This process utilized introduction of hydrogenperoxide into a sidestream of the water requiring treatment. This wasfollowed by introducing acetic anhydride, whereupon PAA was generatedin-situ. It was found that acetic anhydride preferentially reacted withhydrogen peroxide rather than undergo undesirable hydrolysis with water.Within 20 minutes, up to 3000 ppm of PAA was generated in the sidestreamwhich was then reconstituted with the main body of water and dilutedfurther. All processes that employ acetic anhydride suffer thelimitation that acetic anhydride is expensive, very corrosive, anirritant, and highly flammable.

Yet another process for generating non-equilibrium solutions of PAA onsite at the point-of-use is disclosed in WIPO International PublicationNo. WO 01/46519 A1. This process utilized the metering of an aqueoussolution of hydrogen peroxide into an agitated tank and co-metering asolid dry source of tetraacetylethylenediamine (TAED) from astorage-hopper using a screw feeder. The agitator kept the solid TAEDsuspended in the hydrogen peroxide solution which was then fed to anin-line static mixer where aqueous sodium hydroxide was introduced. Themixture was then directed through 200 meters of coiled tubing immersedin a cooling tank so that the temperature rise accompanying theexothermic reaction was contained. Upon exiting the coiled tubing, themixture containing PAA could be directed to the water requiringtreatment. Disadvantages of this approach include the difficulty ofaccurately metering a solid and a liquid simultaneously, and the highcapital equipment cost of the metering system, electronic controllers,agitation tank, coiled tubular reactor, and the cooling system.

Thus, there is a need for a method to make non-equilibrium PAA on siteat the point-of-use that addresses the above problems.

B. Solid PAA Bleaches and Stain Removers

PAA is also used in laundry bleaching applications where it is generatedin-situ in the laundry wash water. The PAA is typically produced from asolid source of hydrogen peroxide, such as sodium percarbonate or sodiumperborate. The hydrogen peroxide must be in the presence of a solidacetyl precursor, most typically, tetraacetyletbylenediamine (TAED).When dissolved in laundry wash water, the TAED undergoes a perhydrolysisreaction with hydrogen peroxide to form PAA. TAED is the preferredacetyl precursor because it possesses low toxicity, is of lowenvironmental impact, and is readily biodegradable. However, TAED-basedlaundry bleaches have several problems. First, of the four acetyl groupson TAED, only two are known to be available for perhydrolysis, makingTAED an expensive acetyl precursor on a weight basis. Second, TAED haslow water solubility, especially at the cooler water temperaturebleaching cycles that are less damaging to fabrics. This is a majordrawback, as current consumer trends in energy conservation are towardsbleaching laundry fabrics with cool temperature water, rather thanheated water. Undissolved TAED in cool temperature water is lessunavailable as an acetyl precursor tor the dissolved source of hydrogenperoxide and can even deposit on fabrics, necessitating a separate rinsestep to remove it. Third, over time, when exposed to high humidity,solid TAED can react with the solid source of hydrogen peroxide and thefree water to form PAA, as well as degrade the activity, making it lesseffective over time. Because tile PAA is volatile. It imparts anundesirable pungent odor to the product. Thus, there is a need for asolid, peroxygen bleach that overcomes the deficiencies of theTAED-containing bleaches.

SUMMARY OF THE INVENTION

In an embodiment, liquid compositions for use in generatingnon-equilibrium solutions of PAA are provided. These hydrogenperoxide-acetyl precursor solutions comprise a solution of aqueoushydrogen peroxide, a liquid acetyl precursor that is soluble in aqueoushydrogen peroxide, a trace amount of peracetic acid, and water. Apreferable acetyl precursor is triacetin, which displays an unexpectedlyhigh sol ability in hydrogen peroxide. These hydrogen peroxide-acetylprecursor solutions may be used for generating a non-equilibriumsolution of peracetic acid for use as a disinfectant or sanitizer on asite having a point-of-use of peracetic acid.

The hydrogen peroxide-acetyl precursor solutions are advantageous inthat they are formulated such that sufficient acetyl precursor can bedissolved in an amount of hydrogen peroxide that would fullyperhydrolyze all of the acetyl groups of the acetyl precursor.Moverover, the hydrogen peroxide component of these compositions isremarkably stable. These compositions overcome one or more problems ofthe known prior art, and are free of the regulatory reporting,permitting, and shipping restrictions that govern equilibrium PAAproducts.

In another embodiment, a method of preparing a hydrogen peroxide-acetylprecursor solution is provided. The method comprises introducing aliquid acetyl precursor that is soluble in aqueous hydrogen peroxide toa solution of aqueous hydrogen peroxide; and allowing the acetylprecursor and the aqueous hydrogen peroxide to mix to form a hydrogenperoxide-acetyl precursor solution.

A further embodiment is a method of continuously or intermittentlygenerating a non-equilibrium solution of peracetic acid on a site havinga point-of-use of peracetic acid for use as a disinfectant or sanitizer.Water is provided on the site having the point-of-use. The water may bea flowing aqueous stream or it may be contained in a mixing tank orother vessel. A hydrogen peroxide-acetyl precursor solution is providedon the site having the point-of-use. In one embodiment, the liquidacetyl precursor is triacetin and the solution that is formed is ahydrogen peroxide-triacetin solution. The hydrogen peroxide-acetylprecursor solution may be prepared off site and then transported to thesite having the point-of-use, or the acetyl precursor and the aqueoushydrogen peroxide may be transported to the site having the point-of-useand then used to prepare the hydrogen peroxide-acetyl precursor solutionon the site. The hydrogen peroxide-acetyl precursor solution is thenintroduced to the water. Alternatively, and in another embodiment, theacetyl precursor and the aqueous hydrogen peroxide may be introduced tothe water separately, either sequentially, with either one first, orsimultaneously. The hydrogen peroxide-acetyl precursor solution and thewater are mixed to form a mixture. An aqueous source of an alkali metalor earth alkali metal hydroxide, such as sodium hydroxide, is providedon the site having the point-of-use. The aqueous source of an alkalimetal or earth alkali metal hydroxide is added to the mixture.Alternatively, and in another embodiment, the aqueous source of alkalimetal or earth alkali metal hydroxide may be added simultaneously withthe hydrogen peroxide-acetyl precursor solution or with the acetylprecursor and the aqueous hydrogen peroxide, to the water. A reactionmedium comprising a non-equilibrium solution of peracetic acid isformed. In the reaction medium, the hydrogen peroxide reacts with theacetyl precursor to form peracetic acid. Almost instantaneously, anon-equilibrium solution of PAA is formed. Within about 30 seconds toabout five minutes, the amount of hydrogen peroxide and acetyl precursorthat are converted into peracetic acid is maximized. When triacetin isused as the acetyl precursor and assuming all three acetyl groups arereacted, about 40.9% to about 85.7% of the triacetin is converted intoperacetic acid, and the percent of hydrogen peroxide remaining is about0.078% to about 1.88%. The reaction medium may optionally be sampled atvarious times after the addition of the aqueous source of alkali metalor earth alkali metal hydroxide to determine the time required tomaximize the amount of hydrogen peroxide and acetyl precursor that areconverted into peracetic acid.

The non-equilibrium solutions of PAA that are farmed comprise PAA,unreacted hydrogen peroxide, unreacted acetyl precursor, the product ofthe perhydrolysis reaction of the acetyl precursor, the aqueous sourceof alkali metal or earth alkali metal hydroxide, and water. Theperacetic acid solutions are alkaline, having a pH of about 11.2 toabout 13.37. The reaction is remarkably fast, proceeds with a highconversion of the acetyl precursor into PAA. This method producessolutions with a high level of PAA, from about 1% to about 7.1%.

The PAA solution is introduced to the receiving water at thepoint-of-use. It may be introduced immediately, of stabilized with theaddition of a source of acid and used throughout a working day. Thereceiving water may be water used in the dairy, food, and beverageprocessing industries for clean-in-place pipeline and equipmentcleaning; for fruit and vegetable washing; and in the treatment of meat,poultry, and seafood products. The receiving water may also be coolingwater, oil and gas process water, or municipal wastewater. Other usesinclude slime and biofilm removal in papermaking processes.

This method addresses one or more: problems of the known prior art. Themethod is easy to perform, inexpensive to operate, and requires onlybasic and common equipment. The method is safe, in that it does notisolate pure PAA, and there is no possibility of a catastrophic eventdue to an equipment failure, such as over-pressurization or explosions.When triacetin is used as the acetyl precursor, it is inexpensive,non-toxic, safe, non-corrosive, non-irritating, non-flammable,sanctioned as Generally Recognized as Safe (GRAS) by the FDA, andconverted quickly and with a high conversion rate into PAA. The methoddoes not require the use of perhydrolase enzymes, acetic acid, or aceticanhydride, all of which suffer from the aforementioned limitations andproblems. The method generates a PAA product that does not containammonium hydroxide. The method can be performed to generate a PAAproduct in a continuous or intermittent fashion. Further, the methodallows the end-user the choice of utilizing the on site generated PAAimmediately or later over the coarse of a working day.

In another embodiment, a freely-flowable, solid peroxygen compositionfor use in laundry bleaching and stain removal is provided. The solidcomposition comprises a liquid acetyl precursor, a water-soluble solidsource of hydrogen peroxide, and a water-soluble: solid source ofalkalinity. The liquid acetyl precursor is preferably triacetin Thecomposition produces peracetic acid upon being introduced to water. Upondissolution, the solid hydrogen peroxide source releases hydrogenperoxide and the solid source of alkalinity dissolves to increase thepH, resulting in the formation of peracetic acid from the reaction, ofthe hydrogen peroxide and the acetyl precursor.

The solid composition is used as a bleaching agent and a stain removerfor the treatment of articles such as fabrics, dentures, textilegarments, and equipment used in the food and beverage industry. Thesolid composition is advantageous in that it does not give rise to anundesirable PAA odor upon storage, contains an acetyl precursor thatefficiently utilizes the acetyl groups it contains, and has a highsolubility in cool temperature water which quickly and efficientlyproduces PAA without the need for elevated water temperatures. Moreover,the acetyl precursor used in making the solid composition may also beused in preparing the liquid compositions described in section 3 above,streamlining manufacturing practices by using the same acetyl precursoras an ingredient in liquid as well as solid compositions.

Surprisingly, this freely-flowable, solid composition includes a liquidacetyl precursor, triacetin. In addition, it is surprising that thiscomposition does not produce a strong odor of peracetic acid duringstorage.

In another embodiment, a method of preparing the freely-flowable, solidperoxygen composition for use in laundry bleaching and stain removal isprovided.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic representation of an example of a system that, maybe used to continuously or intermittently generate PAA for on a sitehaving a point-of-use of peracetic acid In another embodiment, afreely-flowable, solid peroxygen composition for use in laundrybleaching and stain removal is provided according to an embodiment.

DETAILED DESCRIPTION OF THE INVENTION

1. Definitions

The terms “PAA” and “peracetic acid” mean peroxyacetic acid or peraceticacid, and/or the conjugate base of peracetic acid (the peracetate ion).

The terms “percent” and “%” mean weight percent, except when referringto the percent converted.

The term “receiving water” means the water that is being treated.

The term “point-of-use” means the location where the peracetic acidenters the receiving water.

2. Experimental Methods

PAA and hydrogen peroxide in solution were determined using the cericsulfate-sodium thiosulfate method. The method involves adding a knownweight of sample containing the PAA and hydrogen peroxide (or dilution)to a beaker containing 50 ml of chilled 0.9 N sulfuric acid. Using atransfer pipette, 1-2 grams is accurately weighed to a sample cup andreverse osmosis (RO) or deionized water is added to provide a workablevolume. Five drops of ferrous indicator is then added with stirring, andthe sample is then titrated with 0.1 N ceric sulfate until the sampleturns from purple to blue. The volume of ceric sulfate required in mL isrecorded. Then, one or two small scoops of potassium iodide are added tothe sample cup, which turns the solution dark brown. The sample is thentitrated with 0.1 N sodium thiosulfate to discharge the brown colorationand form a pale straw coloration. Then, 10-15 drops of 0.5% starchindicator solution is introduced and the sample turns blue-black. Thesodium thiosulfate is then added dropwise until the color transitions toa bright orange. The volume of sodium thiosulfate in mL was recorded.The percent hydrogen peroxide and the percent PAA are calculated asfollows:

${\%\mspace{14mu}{hydrogen}\mspace{14mu}{peroxide}} = \frac{{mL}\mspace{14mu} 0.1N\mspace{14mu}{ceric}\mspace{14mu}{sulfate} \times 0.17}{{wt}.\mspace{14mu}{sample}}$${\%\mspace{14mu}{PAA}} = \frac{{mL}\mspace{14mu} 0.1\; N\mspace{14mu}{sodium}\mspace{14mu}{thiosulfate} \times 0.38}{{wt}.\mspace{14mu}{sample}}$

For kinetic runs which involved measuring the PAA and hydrogen peroxidein samples at one, three, and five minute intervals after adding thereactants together, the generation reaction was quenched by adding asample of the reaction medium to the sulfuric acid. This halted thegeneration reaction and stabilized the PAA and hydrogen peroxide toelevated pH degradation reactions. This permitted the samples to betaken at the appropriate time interval (one, three, and five minutes),and analyzed later.

In circumstances where low concentrations of PAA were used, the modifiedDPD method (U.S. Pat. No. 7,651,724) was employed. This analyticaltechnique is based on a modified DPD (N,N-diethyl-p-phenylenediamine)colorimetric method accepted by the EPA for measuring total chlorine indrinking water and wastewater. It relies on the ability of PAA to behavelike chlorine in that it rapidly and quantitatively oxidizes iodide ion(I⁻) into iodine (I₂) that reacts with a color indicator (DPD), whichturns the solution a shade of pink, the intensity of which isproportional to the concentration of the PAA. A colorimeter is used thatis programmed to measure the intensity (absorbance) of the pinkcoloration and display the result in terms of ppm as Cl₂. A calculationconverts this number into the ppm as PAA, based on the weight ratio ofPAA to Cl₂ (76/71=1.07).

Hydrogen peroxide does not interfere with the measurement for PAAprovided the analysis is completed within 30 seconds of introducing theDPD reagent. In order for the hydrogen peroxide to be measured. It mustbe activated by addition of a sodium, molybdate catalyst and then giventime (six minutes) to react with the I⁻ ion to liberate I₂. Uponaddition of the DPD indicator, the intensity of the pink colorationmeasured by tire colorimeter is now the sum of the PAA and hydrogenperoxide concentrations expressed as ppm Cl₂. Alter subtracting the ppmreading obtained earlier for the contribution due to PAA, a calculationis then used to convert this number into ppm as hydrogen peroxide, andis based on the weight ratio of hydrogen peroxide to Cl₂ (34/71=0.479).

3. Liquid Compositions for Generating Non-Equilibrium Solutions of PAAon a Site Having a Point-of-Use

In an embodiment, liquid compositions for generating non-equilibriumsolutions of PAA on a site having a point-of-use of peracetic acid areprovided. These solutions are referred to as “hydrogen peroxide-acetylprecursor solutions.” These solutions comprise aqueous hydrogenperoxide, a liquid acetyl precursor that is soluble in aqueous hydrogenperoxide, a trace amount of peracetic acid, and water.

The hydrogen peroxide-acetyl precursor solutions are prepared by thefollowing steps.

-   -   (a) Introducing a liquid acetyl precursor that is soluble in        aqueous hydrogen peroxide to a solution of aqueous hydrogen        peroxide.

Triacetin is a preferable liquid acetyl precursor and 50% hydrogenperoxide is a preferable solution of aqueous hydrogen peroxide. Thetriacetin is preferably added to the 50% hydrogen peroxide at roomtemperature. Alternatively, 70% hydrogen peroxide can be used, but It isnot widely available and requires special handling and transportation.Given that the solubility of triacetin in water is only 7% at 25° C.,triacetin is unexpectedly highly soluble in 50% hydrogen peroxide. Itsolubilizes without an exotherm (temperature increase).

The mole ratio of hydrogen peroxide:triacetin is about 2.98.1 to about12.84:1.

-   -   (b) Allowing the acetyl precursor and the aqueous hydrogen        peroxide to mix to form a hydrogen peroxide-acetyl precursor        solution.

The solution is mixed until a homogenous solution has been formed. Thesolution is allowed to mix by diffusion or by using a mixing device thatis suitable for mixing liquids together. For example, 50% hydrogenperoxide can be introduced to a batch tank equipped with an overheadagitator blade. Triacetin can then be introduced to the 50% hydrogenperoxide when the agitator is in motion so that the components arethoroughly mixed.

The solution that is formed is a hydrogen peroxide-acetyl precursorsolution, which also includes varying amounts of water, depending on theformulation used. When triacetin is used as the liquid acetyl precursor,the solution that is formed is a hydrogen peroxide-triacetin solution.One such hydrogen peroxide-triacetin solution comprises about 23% toabout 40% hydrogen peroxide (from 50% aqueous hydrogen peroxide), about20% to about 52% triacetin, water, and a trace amount of PAA that isformed within the first day of preparing the hydrogen peroxide-acetylprecursor solution. The pH is about 1.46 to about 2.2 and no deliberateattempt is made to adjust the pH further.

A preferable hydrogen peroxide-triacetin solution comprises about 27.15%hydrogen peroxide (from 50% aqueous hydrogen peroxide), about 45.67%triacetin, water, and a trace amount of PAA that is formed within thefirst day of preparing the hydrogen peroxide-acetyl precursor solution.The mole ratio of hydrogen peroxide:triacetin is about 3.8:1.

The hydrogen peroxide-acetyl precursor solutions prepared by this methodmay be used to generate non-equilibrium solutions of PAA on a sitehaving a point-of-use of peracetic acid, in the methods described insection 4 below. The hydrogen peroxide-acetyl precursor solutions may betransported in any container suitable for transporting liquids, such asplastic tote bins of 275-330 gallons, drums of 15-55 gallons,five-gallon pails, one-gallon jugs, or other containers.

Example 1

Triacetin (83.05 g) was added to 50% hydrogen peroxide solution (75 g)to form 158.05 g of a mixture. There was no evolution of gas indicatingthe hydrogen peroxide had decomposed to oxygen, nor was there anyexotherm indicating that a chemical reaction had occurred. The solutiondid not turn oily or cloudy but remained clear. The solution wascalculated to comprise 23.73% hydrogen peroxide and 52.55% triacetin,with the balance being water, and had a measured pH of 2.2. The moleratio of hydrogen peroxide to triacetin was calculated to be 2.98:1.Titration of the solution immediately upon preparation yielded 24.1%hydrogen peroxide, which is within experimental error of the calculatedamount of hydrogen peroxide.

This experiment showed that triacetin is remarkably soluble in 50%hydrogen peroxide. The solubility of triacetin was found to be at least52.55%. This is surprising, given that the solubility of triacetin inwater is only 7% at 25° C.

In order to test the stability of the mixture, the amount of hydrogenperoxide remaining and the amount of PAA generated was tracked forseveral months. The mixture was held at ambient temperature away fromsources of light. Table I summarizes the data.

TABLE I % Hydrogen % PAA Day # Peroxide Remaining Generated 1 23.79 0.0029 23.32 1.28 57 22.56 2.36 92 21.06 4.22 120 19.54 6.05 134 18.57 6.87

Table I shows that although there was a steady depletion in hydrogenperoxide, it was accompanied by an increase in PAA. By the end of the134-day study, the composition had lost 5.22% hydrogen peroxide. Had allof the depleted hydrogen peroxide gone towards the generation of PAA,11.67% PAA would have been generated. Because 6.87% PAA was generated,unaccounted losses of hydrogen peroxide amounted to 2.15%. This loss ofhydrogen peroxide was surprisingly small given that hydrogen peroxide isoften used to destroy organic compounds by oxidation and the compositionoriginally contained 52.55% of triacetin, an organic compound.

Example 2

A formulation containing hydrogen peroxide and triacetin in a mole ratioof 12.84:1 was prepared by adding triacetin (100.0 g) to 50% hydrogenperoxide (400.0 g) so that the mixture was 40% hydrogen, peroxide and20% triacetin, with the balance being water. The pH of the solution was1.46 and the pH of a 1:100 dilution was 3.69. To accelerate storagecharacteristics, the sample was placed in an incubator set for 86-87° F.Table II shows the percent of hydrogen peroxide remaining and thepercent of PAA generated over a period of more than six months.

TABLE II % Hydrogen Peroxide % PAA Days of Study Remaining Generated 140.21 0.004 33 38.02 3.499 54 35.5 5.992 96 29.27 8.36 127 25.05 6.66173 18.49 4.43 201 15.67 3.51

Table II indicates that after 96 days, the generation of PAA. maximizedat 8.36% and corresponded to a loss of 10.94% hydrogen peroxide. Had allof the depleted hydrogen peroxide gone toward the generation of PAA,24.45% PAA would have been generated. Because only 8.36% PAA wasgenerated, unaccounted losses of hydrogen peroxide amounted to 7.2%.

Example 3

A formulation containing hydrogen peroxide and triacetin in a mole ratioof 5.8:1 was prepared by adding triacetin (37.5008 g) to 50% hydrogenperoxide 165.2504 g) so that the mixture was 31.75% hydrogen peroxideand 36.5% triacetin, with the balance being water. The pH of thesolution was 1.57 and the pH of a 1:100 dilution was 5.17. To acceleratedegradation, the sample was placed in an incubator set for 86-87° F.Table III shows the percent of hydrogen peroxide remaining and thepercent of PAA generated over a period of six days.

TABLE III % Hydrogen Peroxide % PAA Days of Study Remaining Generated 131.72 0.33 6 31.63 0.716

In this study, after six days, the mixture had lost only 0.09% hydrogenperoxide, yet had generated an additional 0.386% PAA. Had all the lossof hydrogen peroxide been due to the formation of PAA, only anadditional 0.201% would have been generated. It is clear that theanalytical methods employed for solutions that are high in hydrogenperoxide but low in PAA are subject to detection limit errors.

Example 4

A formulation containing hydrogen peroxide and triacetin in a mole ratioof 3.2:1 was prepared by adding triacetin (35.0 g) to 50% hydrogenperoxide (35.0 g) so that the mixture was 25% hydrogen peroxide and 50%triacetin, with the balance being water. The pH of the solution was 1.66and the pH of a 1:100 dilution was 4.09. To accelerate degradation, thesample was placed in an incubator set for 86-87° F. Table IV shows thepercent of hydrogen peroxide remaining and the percent of PAA generatedover a period of 22 days.

TABLE IV % Hydrogen Peroxide % PAA Days of Study Remaining Generated 125 0.62 8 24.51 1 15 24.17 1.17 22 23.68 1.14

Table IV indicates that after 15 days, the generation of PAA maximizedat 1.17% and corresponded to a loss of 0.83% hydrogen, peroxide. Had allof the depleted hydrogen peroxide gone toward the generation of PAA,1.86% PAA would have been generated. Because only 1.17% PAA wasgenerated, unaccounted losses of hydrogen peroxide amounted to 0.31%.

Example 5

A formulation containing hydrogen, peroxide and triacetin in a moleratio of 4.8:1. was prepared by adding triacetin. (37.50 g) to 50%hydrogen peroxide (56.25 g) so that the mixture was 30% hydrogenperoxide and 40% triacetin, with the balance being water. The pH of thesolution was 1.67 and the pH of a 1:100 dilution was 4.62. To acceleratedegradation, the sample was placed in an incubator set for 86-87° F.Table V shows the percent of hydrogen peroxide remaining and the percentof PAA generated over a period of 43 days.

TABLE V % Hydrogen Peroxide % PAA Days of Study Remaining Generated 130.08 0.38 8 29.85 0.784 15 29.63 1.22 22 29.37 1.71 29 28.76 2.26 3628.67 2.78 43 28.31 3.41

Table V shows that although there was a steady depletion in hydrogenperoxide, it was accompanied by the associative increase of PAA. At theend of the 43-day study, the composition had lost 1.77% hydrogenperoxide. Had all of the depleted hydrogen peroxide gone toward thegeneration of PAA, 3.96% PAA would have been generated. Because only3.41% PAA was generated, unaccounted losses of hydrogen peroxideamounted to 0.24%.

Example 6

A formulation containing hydrogen peroxide and triacetin in a mole ratioof 6.42:1 was prepared by adding triacetin (25.0007 g) to 50% hydrogenperoxide (50.0007 g) so that the mixture was 33.33% hydrogen peroxideand 33.33% triacetin, with the balance being water. The pH of thesolution was 1.56 and the pH of a 1:100 dilution was 5.15. To acceleratedegradation, the sample was placed in an incubator set for 86-87° F.Table VI shows the percent of hydrogen peroxide remaining and thepercent of PAA generated over a period of 36 days.

TABLE VI % Hydrogen Peroxide % PAA Days of Study Remaining Generated 133.13 0.81 8 32.88 1.35 15 32.61 1.88 22 31.69 2.58 29 31.75 3.03 3631.29 3.28

Table VI shows that although there was a steady depletion in hydrogenperoxide, it was accompanied by an associative increase of PAA. At theend of the 36-day study, the composition had lost 1.84% hydrogenperoxide. Had all of the depleted hydrogen peroxide gone toward thegeneration of PAA, 4.11 % PAA would have been generated. Because only3.28% PAA was generated, unaccounted losses of hydrogen peroxideamounted to 0.37%.

Example 7

A 30-gallon batch of 50% hydrogen peroxide and triacetin was prepared byblending 137 lbs triacetin with 163 lbs 50% hydrogen peroxide so thatthe mixture was 27.15% hydrogen peroxide and 45.67% triacetin, with thebalance being water. Thus, the mole ratio of hydrogen peroxide:triacetinwas 3.8:1. The mixture was stored in an opaque drum, in a non-climatecontrolled environment. On storage, the mixture slowly formed PAA in thecontainer. Since this reaction of hydrogen peroxide to PAA does notrepresent a destructive loss of total peroxygen, to determine the truestability of the hydrogen peroxide, both the hydrogen peroxide and theperacetic acid generated must be quantified and reported as totalperoxygen recovered.

After 295 days of storage, the mixture was analyzed for total peroxygenrecovered (expressed as hydrogen peroxide) to determine the percent lossof peroxygen. Using the ceric Sulfate-iodometric titration method, thePAA generated and the hydrogen peroxide remaining were measured. Thetotal peroxygen recovered after 295 days and the theoretical initialconcentrations are shown in Table VII. All peroxygen is expressed as %hydrogen peroxide.

TABLE VII Initial Theoretical % % (after 295 days) Hydrogen PeroxideRecovered 27.17 15.20 PAA formed 0 15.57 Hydrogen Peroxide Reacted to 06.97 form PAA Total Recovered Hydrogen 27.17 22.17 Peroxide TotalHydrogen Peroxide 5.00 Unproductive Loss

After 295 days, 22.17% of the total peroxygen was recovered as eithertitratable hydrogen peroxide or hydrogen peroxide reacted to form PAA.To determine the stability of the peroxygen in the mixture, the totalrecovered hydrogen, peroxide after 295 days (22.17%) was subtracted fromthe total recovered hydrogen peroxide of the initial theoretical value(27.17%). The result, 5%, is the loss of peroxygen (expressed ashydrogen peroxide) after 295 days of storage in a non-climate controlledenvironment.

4. Methods of Generating Non-Equilibrium PAA on Site at the Point-of-Use

Methods of continuously or intermittently generating non-equilibriumsolutions of PAA on a site having a point-of-use of PAA for use as adisinfectant or sanitizer, using a source of water that is an aqueousstream or by a batch process using water in a container, are provided.

In one embodiment, a method of continuously or intermittently generatingnon-equilibrium solutions of PAA on a site having a point-of-use, usinga source of water that is an aqueous stream, comprises the followingsteps.

-   -   (a) Providing water.

Flowing water is provided on a site having a point-of-use of peraceticacid.

The water may be flowing in, for example, a pipe, a flume, a canal, orother types of aqueous streams. The water pressure should be regulatedand the flow rate should be monitored or measured. Any suitable flowmeter may be used, such as a rotameter, a magnetic flow meter, anultrasonic flow meter, a Doppler flow meter, a differential-pressureflow meter, a turbine flow meter, or a Coriolis flow meter.

The water should be softened, deionized, or of sufficient low hardnessthat it will not precipitate calcium salts when the alkali metal orearth alkali metal hydroxide is introduced in step (d).

-   -   (b) Introducing a hydrogen peroxide-acetyl precursor solution to        the water.

A hydrogen peroxide-acetyl precursor solution is provided on the sitehaving the point-of-use of the PAA. The hydrogen peroxide-acetylprecursor solution may be prepared by the steps set forth in section 3above. The hydrogen peroxide-acetyl precursor solution may be preparedoff site and then transported to the site having the point-of-use, orthe acetyl precursor and the aqueous hydrogen peroxide may betransported to the site having the point-of-use and used to prepare thehydrogen peroxide-acetyl precursor solution on the site.

A preferable liquid acetyl precursor is triacetin. When triacetin isused, a hydrogen peroxide-triacetin solution is introduced.

The hydrogen peroxide-acetyl precursor solution is introduced to theflowing water in an amount such that the hydrogen peroxide-acetylprecursor solution is about 5.6% to about 22.5% of the total.

The hydrogen peroxide-acetyl precursor solution is pumped from itscontainer into the aqueous water stream, for example, through aninjection quill mounted on the pipe. Any suitable pump capable ofovercoming the pressure of the water flowing in the pipe may be used.Examples include a solenoid-driven or air-driven diaphragm pump or aperistaltic pump. The rate at which the hydrogen peroxide-acetylprecursor solution is pumped into the flowing water is governed by acontroller that is interfaced to a flow meter that is measuring the flowof the water. In this way, the rate at which the hydrogenperoxide-acetyl precursor solution is pumped may be matched to the flowof the water in the aqueous stream. If the flow of the water slows, therate at which the hydrogen peroxide-acetyl precursor solution is pumpedshould slow accordingly. If the flow of the water stops, the hydrogenperoxide-acetyl precursor pump should stop.

As an alternative to step (b), the liquid acetyl precursor and thesolution of aqueous hydrogen peroxide may be introduced to the waterseparately, either simultaneously or sequentially. If they areintroduced sequentially, either one may be added first. If the liquidacetyl precursor and the aqueous hydrogen peroxide are introducedseparately, rather than as an hydrogen peroxide-acetyl precursorsolution, then in step (c) the liquid acetyl precursor and the aqueoushydrogen peroxide are mixed with the water to form a mixture.

-   -   (c) Mixing the hydrogen peroxide-acetyl precursor solution and        the water to form a mixture.

Any mixing device suitable for mixing liquids may be used. An example isa static mixer located just after the point that the hydrogenperoxide-acetyl precursor solution is introduced to the flowing water.One type of static mixer utilizes a non-moving element such as a seriesof baffles. As the mixture flows through the static mixer under themotive force of the flowing water, the non-moving element divides theflow several times to provide radial mixing. Another type of staticmixer utilizes a series of obstructions, such as column packing or glassbeads, provided there is a low differential pressure drop across themixer. The obstructions provide for turbulent mixing of the hydrogenperoxide-acetyl precursor solution and the flowing water. The mixingshould yield a homogeneous solution with no concentration gradientsbefore the next step is performed. The velocity of the water willdetermine the time it takes to complete the mixing and the efficiency ofthe mixing. For example, with ¾″ pipe, a static mixer of ¾″ diameter and6″ long, and a velocity of about 1 gal/mm., mixing should beaccomplished in less than about one second.

-   -   (d) Adding an aqueous source of an alkali metal or earth alkali        metal hydroxide to the mixture.

An aqueous source of an alkali metal or earth alkali metal hydroxide isprovided on the site having the point-of use. A preferable aqueoussource of an alkali metal hydroxide is sodium hydroxide, and 50% sodiumhydroxide is most preferable. Other suitable alkali metal hydroxidesinclude 45% potassium hydroxide.

Sufficient 50% NaOH is added to the flowing mixture such that the amountof sodium hydroxide is about 1.82% to about 7.28% of the total amount.When the acetyl precursor is triacetin, a preferred mole ratio ofNaOH:hydrogen peroxide:triacetin is about 4.2:3.8:1.

The 50% NaOH solution is added to the mixture by pumping it from itscontainer with a suitable pumping device and into the mixture through aninjection quill mounted on the pipe. Any suitable pump capable ofovercoming the hydraulic pressure of the pipe may be used. Examplesinclude a solenoid-driven or air-driven diaphragm pump or a peristalticpump.

The rate at which the 50% NaOH solution, is pumped into the pipe isgoverned by the same controller that is interfaced to both the flowmeter that is measuring the flow of the mixture and the pump controllingthe rate of introduction of the hydrogen peroxide-acetyl precursorsolution. In this way, the rate at which the 50% NaOH solution isintroduced may be matched to both the flow of the mixture and the rateof introducing the hydrogen peroxide-acetyl precursor solution. If theflow of the mixture slows for any reason, the rate at which the 50% NaOHsolution is pumped should slow accordingly. If the flow of the mixturestops, the 50% NaOH pump should stop as well.

Step (d) may be performed after step (e), or it may be performedsimultaneously with step (b).

-   -   (e) Forming a reaction medium comprising a non-equilibrium        solution of peracetic acid.

The reaction median that is formed in this step almost instantaneouslyforms a non-equilibrium solution of PAA. The hydrogen peroxide reactswith the acetyl precursor to form peracetic acid. Depending upon thetemperature of the water, the efficiency of mixing, and the mole ratioof NaOH:hydrogen peroxide:acetyl precursor employed, the amount ofhydrogen peroxide and acetyl precursor that are converted into PAA ismaximized within about 30 seconds to about five minutes.

The non-equilibrium, solutions of PAA prepared by this method comprisePAA, unreacted hydrogen peroxide, unreacted acetyl precursor, theproduct of the perhydrolysis reaction of the acetyl precursor, theaqueous source of alkali metal or earth alkali metal hydroxide, andwater. When the acetyl precursors is triacetin, the product of theperhydrolysis reaction is 1, 2, 3-propanetriol (glycerine).

This method may also include an optional step after step (e) of samplingthe reaction medium at various times after the addition of the aqueoussource of alkali metal or earth alkali metal hydroxide to determine thetime required under the existing conditions to maximize the amount ofhydrogen peroxide and acetyl precursor that are converted into PAA. Thismay be accomplished by directing the flow of the reaction medium througha series of residence chambers equipped with sampling ports. Theresidence chambers are designed to be of sufficient volume such that acertain amount of time has elapsed since the introduction of the 50%NaOH. Thus, at any given flow rate in the pipe, the first residencechamber is of a volume such that 30 seconds have elapsed since theintroduction of 50% NaOH, one minute has elapsed by the time the flowreaches the sampling port immediately after the second residencechamber, and additional time elapses by the time the flow reaches theremaining sampling ports. Up to four residence chambers and samplingports may be placed in series such as this to provide the user withabout 30 seconds to five minutes of residence time after tireintroduction of the 50% NaOH. Once the flow of the reaction medium hasbeen established, samples are drawn from all four sampling portsassociated with the residence chambers and analyzed for peracetic acid.The sample which registers the highest amount of peracetic acid isdeemed to be drawn from the sampling port associated with the residencechamber corresponding to the time of maximum conversion of the acetylprecursor into peracetic acid. At this point, the entire flow ofreaction medium is directed through the sampling point of maximumconversion of acetyl precursor and to the point-of-use.

In another embodiment, a method of continuously or intermittentlygenerating a Non-equilibrium solution of PAA on a site having a thepoint-of-use in a batch process comprises the following steps:

-   -   (a) Providing water.

A container of water, such as a mixing tank or other vessel, is providedon a site having a point-of-use of peracetic acid. The water should besoftened, deionized, or of sufficient low hardness that it will notprecipitate calcium salts when the alkali metal or earth alkali metalhydroxide is introduced in step (d).

-   -   (b) Introducing a hydrogen peroxide-acetyl precursor solution to        the water.

A hydrogen peroxide-acetyl precursor solution is provided on the sitehaving the point-of-use of the PAA. The hydrogen peroxide-acetylprecursor solution may be prepared by the steps set forth in section 3above. The hydrogen peroxide-acetyl precursor solution may be preparedoff site and then transported to the site having the point-of-use, orthe acetyl precursor and the aqueous hydrogen peroxide may betransported to the site having the point-of-use and used to prepare thehydrogen peroxide-acetyl precursor solution on the site.

A preferable liquid acetyl precursor is triacetin. When triacetin isused, a hydrogen peroxide-triacetin solution is introduced.

The hydrogen peroxide-acetyl precursor solution is introduced to thewater in an amount such that the hydrogen peroxide-acetyl precursorsolution is about 5.6% to about 22.5% of the total.

The hydrogen peroxide-acetyl precursor solution is pumped from itscontainer into the container of water through an injection quill mountedon the side of the container of water. Any suitable pump may be used.Examples include a solenoid-driven or air-driven diaphragm pump or aperistaltic pump.

As an alternative to step (b), the liquid acetyl precursor and thesolution of aqueous hydrogen peroxide may be introduced to the waterseparately, either simultaneously or sequentially. If they areintroduced sequentially, either one may be added first. If the liquidacetyl precursor and the aqueous hydrogen peroxide are introducedseparately, rather than as an hydrogen peroxide-acetyl precursorsolution, then in step (c) the liquid acetyl precursor and the aqueoushydrogen peroxide are mixed with the water to form a mixture.

-   -   (c) Mixing the hydrogen peroxide-acetyl precursor solution and        the water to form a mixture.

Any mixing device suitable tor mixing liquids may be used. An example isan overhead stirrer, such as an agitator blade. The container of wateris equipped with a baffle to assist the process of mixing. The mixingshould yield a homogeneous solution with no concentration gradientsbefore the next step is performed.

-   -   (d) Adding an aqueous source of an alkali metal or earth, alkali        metal hydroxide to the mixture.

An aqueous source of an alkali metal or earth alkali metal hydroxide isprovided on the site having the point-of-use. A preferable aqueoussource of an alkali metal hydroxide is sodium hydroxide, and 50% sodiumhydroxide is most preferable. Other suitable alkali metal hydroxidesinclude 45% potassium hydroxide.

Sufficient 50% NaOH is added to the mixture such that the amount ofsodium hydroxide is about 1.82% to about 7.28% of the total amount. Whenthe acetyl precursor is triacetin, a preferred mole ratio ofNaOH:hydrogen peroxide:triacetin is about 4.2:3.8:1.

The 50% NaOH solution is added to the mixture by pumping it from itscontainer with a suitable pumping device and into the mixture through aninjection quill mounted on the side of the container of water. Anysuitable pump may be used. Examples include a solenoid-driven orair-driven diaphragm pump or a peristaltic pump.

Step (d) may be performed alter step (c), or it may be performedsimultaneously with step (b).

-   -   (e) Forming a reaction medium comprising a non-equilibrium        solution of peracetic acid.

The reaction medium that is formed in this step almost instantaneouslyforms a non-equilibrium solution of PAA. The hydrogen peroxide reactswith the acetyl precursor to form peracetic acid. Depending upon thetemperature of the water, the efficiency of mixing, and the mole ratioof NaOH:hydrogen peroxide:acetyl precursor employed, the amount ofhydrogen peroxide and acetyl precursor that are converted into PAA ismaximized within about 30 seconds to about five minutes.

The non-equilibrium solutions of PAA prepared by this method comprisePAA, unreacted hydrogen peroxide, unreacted acetyl precursor, theproduct of the perhydrolysis reaction of the acetyl precursor, theaqueous source of alkali metal or earth alkali metal hydroxide, andwater. When the acetyl precursors is triacetin, the product of theperhydrolysis reaction is 1, 2, 3-propanetriol (glycerine).

While not wishing to be bound by theory, it is believed that underelevated pH conditions created by the addition of a source of alkalimetal hydroxide or earth alkali metal hydroxide, hydrogen peroxidedissociates according to the following equation:H₂O₂=H⁺+HO₂ ⁻

The perhydroxyl anion (HO₂ ⁻) then affects nucleophilic substitutionreactions on the carbonyl groups of the acetyl precursor in aperhydrolysis reaction to form peracetic acid and the product of theperhydroloysis reaction of the acetyl precursor. When the acetylprecursor is triacetin and all three acetyl groups are reacted, then theproduct of the perhydrolysis reaction is 1, 2, 3-propanetriol(glycerine).

In these methods, the perhydrolysis reaction is rapid and the maximumamount of PAA is generated within about 30 seconds to about five minutesat ambient temperature. The methods efficiently utilize the acetylprecursor and the source of hydrogen peroxide. When triacetin is used,assuming all three acetyl groups are reacted, about 40.9% to about 85.7%of the triacetin is converted into PAA. The percent of hydrogen peroxideremaining is about 0.078% to about 1.88%.

The non-equilibrium solutions of PAA prepared by these methods haveseveral unique characteristics. The PAA solutions have high levels ofPAA, from about 1% to about 7.1%. In addition, the PAA solutions arealkaline, having a pH of about 11.2 to about 13.37.

The non-equilibrium solutions of PAA may be immediately introduced tothe receiving water at the point-of-use. Alternatively, the solutionsmay be stabilized by halting the decomposition of the PAA by adding asource of acid to lower the elevated pH of the reaction medium caused bythe addition of an alkali metal or earth alkali metal, hydroxide, and toprovide neutral to mildly acid pH conditions to stabilize the PAA toelevated pH degradation. The acid-stabilized PAA solutions can then bestored and used at the point-of-use as required throughout a workingday.

The non-equilibrium PAA solutions produced by these methods can beadvantageously used wherever traditional equilibrium solutions of PAAare used. Thus, the PAA solutions may be used as a disinfectant andsanitizer in the dairy, food, and beverage processing industries forclean-in-place pipeline and equipment cleaning; for fruit and vegetablewashing; and in the treatment of meat, poultry, and seafood products.These PAA solutions may also be used in the treatment of cooling water,oil and gas process water, and municipal wastewater. Other uses includeslime and biofilm removal in papermaking processes.

For both of the above methods, steps (a) through (e) may be performed ona continuous or intermittent basis. In a continuous basis, the steps areperformed under conditions of steady state, and the PAA solution isproduced at the same rate as a function of time. However, intermittentperforming of steps (a) through (e) is possible if the demand for thePAA solution drops for any reason (e.g., change in working shift or thetarget level of PAA in the receiving water has been achieved), in whichcase, steps (a) through (e) may be discontinued and resumed when thedemand increases.

Example 8

Tests were performed using about one liter of reverse osmosis (RO) orsoftened water which was buffered to an alkaline pH. The bufferingmedia, included 0.1 and 0.2 M Na₂CO₃ solutions, in addition to 0.1 and0.2 M NaOH solutions. Sufficient buffering media was added to the waterin order to achieve the desired pH. The amount of hydrogen peroxide(introduced as 50% hydrogen peroxide) and triacetin used in the tests issummarized in Table VIII. The reactants were introduced to the solutionin one of three ways: simultaneously (referred to in Table VIII as“double”), sequentially (triacetin followed shortly by hydrogenperoxide), or by mixing the hydrogen peroxide and triacetin together andadding them in a single charge (referred to in Table VIII as “mixed”).All testing was performed at ambient temperature as the one-liter beakerwas stirred with a magnetic stir bar. Using the ceric sulfate-iodometrictitration method, the percent of PAA generated and the percent ofhydrogen peroxide remaining were measured five minutes afterintroduction of the reactants to the buffer. The percent of thetriacetin acetyl donor converted to PAA was calculated, assuming allthree acetyl groups were available for perhydrolysis.

TABLE VIII Moles Hydrogen Type of Addition Hydrogen % Peroxide/ (DoublePeroxide Triacetin Hydrogen % Triacetin Mole Sequential or pH of UsedUsed % PAA Peroxide Converted Test # Triacetin Mixed) Buffer (Wt., g)(Wt., g) Generated Remaining to PAA 1 4.99 Double 10.50 8.60 5.53 0.1700.329 29.6% 2 5.47 Double 10.50 8.60 5.04 0.178 0.333 33.9% 3 5.45Double 10.80 8.61 5.07 0.192 0.329 36.4% 4 5.68 Double 11.00 8.87 5.010.201 0.322 38.6% 5 5.72 Double 11.00 9.13 5.12 0.068 0.416 12.8% 6 5.49Double 12.42 8.60 5.02 0.169 0.306 32.4% 7 5.59 Double 12.91 8.60 4.930.320 0.265 62.4% 8 5.53 Double 12.80 8.69 5.04 0.335 0.273 63.9% 9 25.0Double 12.65 9.03 1.16 0.104 0.413 85.9% 10 5.26 Double 12.60 8.70 5.300.298 0.247 54.1% 11 5.52 Sequential 12.83 8.68 5.04 0.276 0.248 52.4%12 5.47 Sequential 12.81 17.11 10.03 0.120 0.371 11.4% 13 28.8 Mixed11.12 8.74 0.973 0.039 0.398 38.9% 14 28.8 Mixed 11.99 8.75 0.974 0.0380.374 37.9% 15 28.8 Mixed 13.02 8.69 0.967 0.055 0.367 55.2% 16 28.8Mixed 7.91 8.70 0.968 0.024 0.435 23.7% 17 28.8 Mixed 11.22 8.76 0.9750.029 0.309 28.4% 18 28.8 Mixed 12.07 8.68 0.966 0.028 0.311 27.7% 1928.8 Mixed 13.22 8.72 0.971 0.026 0.321 25.6% 19 dup 25.2 Mixed 12.978.77 1.12 0.031 0.249 26.5% 20 25.2 Mixed 12.98 9.08 1.16 0.066 0.39354.5% 20 dup 25.5 Mixed 13.00 9.10 1.16 0.074 0.409 61.0% 21 25.2 Mixed13.02 9.10 1.16 0.02 0.261 16.5% 21 dup 25.2 Mixed 12.99 9.12 1.16 0.0170.376 14.0% 22 16.0 Mixed 12.99 5.80 1.16 0.070 0.246 57.7% 23 16.0Mixed 13.05 5.79 1.16 0.013 0.189 10.7% 24 16.0 Mixed 12.55 5.78 1.160.031 0.234 25.6% 25 16.0 Mixed 12.49 5.80 1.16 0.013 0.144 10.7% 2616.0 Mixed 12.01 5.85 1.17 0.016 0.259 13.1% 27 16.0 Mixed 12.05 5.821.16 0.011 0.080 9.0% 28 16.0 Mixed 10.50 0.601 0.120 0.00077 0.028 6.1%29 16.0 Mixed 10.97 0.595 0.119 0.00023 0.021 1.8% 30 16.0 Mixed 10.500.614 0.123 0.00012 0.019 0.9% 31 16.0 Mixed 10.97 0.595 0.119 0.000350.018 2.8%

Table VIII shows that the amount of PAA generated was independent of themethod of introducing the triacetin and hydrogen peroxide to the buffersolutions. It can be seen that the pH of the buffer had a significanteffect on the percent of the triacetin that was converted into PAA. Onlywhen the pH was above 12 was a meaningful percent of the triacetinconverted into PAA.

Example 9

A mixture of triacetin and hydrogen peroxide was prepared by blending50% hydrogen peroxide (63.4%) and triacetin (36.0%). Thus, the moleratio of hydrogen peroxide:triacetin was 5.57:1. The mixture (13.68 g)was added to soft water such that the final solution contained 5 g/L oftriacetin and had a pH of 4.1. Then, in successive experiments,sufficient 50% NaOH was added to the beaker so that the mole ratio ofNaOH:TA was varied from 3:1 (obtained by introducing 5.40 g of 50% NaOH)to 8:1 (obtained by introducing 14.68 g of 50% NaOH). Using the cericsulfate-iodometric titration method, the percent of PAA generated andthe percent of hydrogen peroxide remaining were measured over the next20 minutes. The method was performed in duplicate for each sample point.The averages of the results for the 6:1 mole ratio of NaOH:TA are shownin Table IX.

TABLE IX % PAA % Hydrogen % Triacetin Converted Time (min) GeneratedPeroxide Remaining to PAA (3 acetyls) 0 0.015 0.437 2.9 1 0.275 0.29853.1 3 0.312 0.274 60.2 5 0.326 0.258 62.9 11 0.302 0.233 58.3 21 0.2460.199 47.5

It can be seen that even before the introduction of 50% NaOH, some PAAwas present in solution as a result of being generated in the dilutedmixture of the two components. Upon addition of the NaOH, PAA wasimmediately generated, with the maximum amount of 0.326% occurring atfive minutes, corresponding to a yield of 62.9% assuming all threeacetyl groups of triacetin were available for perhydrolysis.

This exercise was repeated for mole ratios of NaOH:triacetin rangingfrom 3:1 to 8:1. Table X summarizes the next set of data and shows themaximum percent of PAA generated, the time after the addition of NaOHthat it took to reach the maximum percent of PAA generated, the pH afterthe addition of the NaOH, the percent of hydrogen peroxide remaining atthe time of the maximum percent of PAA, and the calculated percent, oftriacetin converted to PAA assuming that all three acetyl groups wereavailable for perhydrolysis.

TABLE X % Triacetin Time at Max % % Hydrogen Converted Mole ratio Max.PAA PAA Peroxide to PAA NaOH:TA (min) Generated Remaining (3 acetyls) pH3:1 3 0.229 0.291 43.8 11.2 4:1 6 0.285 0.251 54.8 11.3 6:1 5 0.3260.258 62.9 11.6 8:1 3 0.335 0.271 64.7 12.2

It can be seen that the amount of PAA generated, and hence theconversion of triacetin into PAA, increased with the increasing moleratio of NaOH:TA. For all four mole ratios employed, the maximum amountof PAA was generated between three and six minutes. The optimum moleratio of NaOH:TA was 6:1 as it resulted in an efficient utilization oftriacetin converted into PAA, and because the pH of the resultingreaction medium would have less impact on the pH of the receiving waterthan the higher pH of the reaction medium resulting from the 8:1 moleratio.

Example 10

A series of experiments was then performed in which the mole ratio ofNaOH:TA was fixed at 8:1 and the mole ratio of hydrogenperoxide-triacetin was varied from 2:1 to 8:1. Triacetin (5 g) was addedto about 965 mL of softened water along with 50.7% hydrogen peroxide insuccessive tests (3.06 g for the 2:1 mole ratio; 6.19 g for the 4:1 moleratio; 9.23 g tor the 6:1 mole ratio; and 12.32 g for the 8:1 moleratio) to yield a solution with a pH of about 4.8-5.5. The volume of themixture was adjusted to 990 mL with softened water. With mixing, 50%NaOH (14.67 g) was introduced. Using the ceric sulfate-iodometrictitration method, the percent of PAA generated and the percent ofhydrogen peroxide remaining were measured over the next 20 minutes. Themethod was performed in duplicate for each sample point The averages ofthe results for the kinetic run employing the mole ratio of 8:6:1NaOH:hydrogen peroxide:TA are shown in Table XI.

TABLE XI % PAA % Hydrogen % Triacetin Converted Time (min) GeneratedPeroxide Remaining to PAA (3 acetyls) 1 0.331 0.317 63.8 3 0.330 0.30363.6 5 0.319 0.303 61.5 10 0.300 0.295 57.8 20 0.256 0.274 49.3

Upon addition, of the NaOH, PAA was immediately generated, with themaximum amount of 0.331% occurring after just one minute, correspondingto a calculated conversion of triacetin into PAA of 63.8%, assuming thatall three acetyl groups of triacetin were available for perhydrolysis.

This exercise was repeated for mole ratios of hydrogenperoxide:triacetin ranging from 2:1 to 6:1. Table XII summarizes thedata and shows the maximum percent of PAA generated, the time after theaddition of NaOH that it took to reach the maximum percent of PAAgenerated, the pH after the addition of the NaOH, the percent ofhydrogen peroxide remaining at the time of the maximum percent of PAA,and the calculated percent of triacetin converted to PAA assuming thatall three acetyl groups were available for perhydrolysis.

TABLE XII Mole Ratio % Triacetin Hydrogen Time at Max % % HydrogenConverted Peroxide: Max. PAA PAA Peroxide to PAA Triacetin (min)Generated Remaining (3 acetyls) pH 2:1 3 0.214 0.079 40.9 12.6 4:1 10.272 0.195 51.9 12.4 6:1 1 0.331 0.317 63.8 12.3 8:1 3 0.374 0.445 72.011.9

It can be seen that the amount of PAA generated, and hence theconversion of triacetin into PAA. Increased with the increasing moleratio of hydrogen peroxide:triacetin. For all four mole ratios employed,the maximum amount of PAA was generated between one and three minutes.The optimum mole ratio of hydrogen peroxide:triacetin was 8:1 as itresulted in the most efficient utilization of triacetin converted intoPAA.

Example 11

A further series of experiments was performed in which the mole ratio ofhydrogen peroxide to triacetin was fixed at 4:1 and the molar ratio ofNaOH to triacetin was varied from 3:1 to 8:1. Triacetin (5 g) was addedto around 975 mL of softened water along with 50.7% hydrogen peroxide(6.18 g) to yield a solution with a pH of 4.8 to 5.3. With mixing, 50%NaOH was introduced in successive tests (5.51 g for the 3:1 mole ratio;7.30 g for the 4:1 mole ratio; 11.03 g for the 6:1 mole ratio; and 14.67g for the 8:1 mole ratio). The volume of the mixture was adjusted to1000 mL with softened water. Using the ceric sulfate-iodometrictitration method, the percent of PAA generated and the percent ofhydrogen peroxide remaining were measured over the next 20 minutes. Themethod was performed in duplicate for each sample point. The averages ofthe results for the kinetic run employing the mole ratio ofNaOH:hydrogen peroxide:triacetin of 4:4:1 are shown in Table XIII.

TABLE XIII % Hydrogen % Triacetin % PAA Peroxide Converted to PAA Time(min) Generated Remaining (3 acetyls) 1 0.247 0.207 47.3 3 0.280 0.17853.6 5 0.292 0.167 55.9 10 0.267 0.142 51.1 20 0.229 0.111 43.8

Upon addition of the NaOH, PAA was immediately generated, with themaximum amount of 0.292% occurring after five minutes, corresponding, toa calculated conversion of 55.9% triacetin into PAA assuming that allthree acetyl groups of triacetin were available for perhydrolysis.

This exercise was repeated tor mole ratios of NaOH:TA ranging from 3:1to 8:1. Table XIV summarizes the data and records the maximum percent ofPAA generated, the time after the addition of NaOH that it took to reachthe maximum percent of PAA generated, the pH after the addition of theNaOH, the percent of hydrogen peroxide remaining at the time of themaximum percent of PAA, and the calculated percent of triacetinconverted to PAA assuming that all three acetyl groups were availablefor perhydrolysis.

TABLE XIV % Triacetin Time at Max % % Hydrogen Converted Mole Ratio Max.PAA PAA Peroxide to PAA NaOH:TA (min) Generated Remaining (3 acetyls) pH3:1 3 0.246 0.202 47.2 11.3 4:1 5 0.292 0.167 55.9 11.6 6:1 3 0.2900.181 55.6 12.2 8:1 3 0.272 0.195 51.9 12.4

It can be seen that the amount of PAA generated maximized when the moleratio of NaOH:hydrogen peroxide:triacetin was 4:4:1. The optimum moleratio of NaOH:hydrogen peroxide:triacetin was 4:4:1 as it resulted in anefficient utilization of triacetin converted into PAA, and because thepH of the resulting reaction medium would have less impact on the pH ofthe receiving water than the higher pH of the reaction medium resultingfrom the 4:6:1 mole ratio of NaOH:hydrogen peroxide:triacetin. For allfour mole ratios employed, the maximum amount of PAA was generatedbetween three and five minutes.

Example 12

In the first test, a mixture of triacetin and hydrogen peroxide wasprepared by blending 50% hydrogen peroxide (54,24%) and triacetin(45.76%), Thus, the mole ratio of hydrogen peroxide:triacetin was3.65:1. The mixture (51.22 g) was dissolved in soft water (911.9 g) in aone-liter beaker to yield a solution with a pH of 6.47. Then, 50% NaOH(36.47 g) was introduced with stirring. Thus, the mole ratio of thecombined mixture of NaOH:hydrogen peroxide:triacetin was 4.2:3.8:1. ThepH of the resulting solution initially measured 12.1. Using the cericsulfate-iodometric titration method, the PAA generated and the hydrogenperoxide remaining were measured over the next 10 minutes. It wasnoticed that the sample temperature rose immediately upon addition ofthe 50% NaOH.

In the second test, the first test was repeated except that the waterwas chilled soft water.

In the third test, the first test was repeated using three times theoriginal amount of hydrogen peroxide:triacetin mixture and three timesthe original amount of 50% NaOH. The mole ratio of the combined mixtureof NaOH:hydrogen peroxide:triacetin remained the same as before, at4.2:3.8:1. The hydrogen peroxide and triacetin mixture (153.96 g) wasintroduced to chilled soft water (735.6 g) in a one-liter beaker toyield a solution with an initial pH of 5.14. Then, 50% NaOH (111.21 g)was introduced. Using the ceric sulfate-iodometric titration method, thePAA generated and the hydrogen peroxide remaining were measured over thenext 10 minutes.

In the fourth test, the first test was repeated using four times theoriginal amount of hydrogen peroxide:triacetin mixture and four timesthe original amount of 50% NaOH. The mole ratio of the combined mixtureof NaOH:hydrogen peroxide:triacetin remained the same as before, at4.2:3.8:1. The hydrogen peroxide and triacetin mixture (204.7 g) wasintroduced to chilled soft water (647.5 g) in a one-liter beaker toyield a solution with an initial pH of 6.32. Then, 50% NaOH (155.4 g)was introduced. Using the ceric sulfate-iodometric titration method, thePAA generated and the hydrogen peroxide remaining were measured over thenext 10 minutes.

Table XV summarizes the results obtained for the four tests and showsthe initial and final solution temperatures, the pH of the solutionafter the addition of the 50% NaOH, the maximum percent of PAAgenerated, the time of maximum PAA generation, and the percent ofhydrogen peroxide remaining.

TABLE XV Initial Final Max. % PAA % Hydrogen Temp. Temp. GeneratedPeroxide Test # (° F.) (° F.) Final pH (time, min) Remaining 1 NM NM12.14 1.71 (1)  0.58 2 38 50 12.67 2.1 (4) 0.43 3 44 88 12.77 6.3 (1)1.18 4 34 92 13.17 7.2 (1) 1.88 NM = not measured

Table XVI shows the percent of hydrogen peroxide convened overall, thepercent of hydrogen peroxide converted to PAA, and the percent oftriacetin converted to PAA (assuming that all three acetyl groups ontriacetin are available tor conversion to PAA) for each of the tests inTable XV.

TABLE XVI % Hydrogen Peroxide % Triacetin % Hydrogen Peroxide Convertedto Converted to Converted PAA (at maximum PAA Test # Overall conversiontime) (3 acetyls) 1 67.8 88.1 69.7 2 68.8 94.4 85.8 3 71.6 94.3 85.7 466.1 88.1 73.8

The data in Tables XV and XVI indicate that far higher amounts of PAAare possible if the 50% sodium hydroxide solution is the last componentof the mixture to be introduced. Further, up to 7.1% PAA was generated,although this solution got hot despite chilling the source water.Generation of the 6.3% PAA solution was very efficient because itrepresented a high 85.7% utilization of triacetin converted into PAA.There was clearly a linear relationship between Test 2, which generated2.1% PAA, and Test 3, which utilized three times more of the reactantsand generated 6.3% PAA, The data in Table XV indicate that the time ofmaximum conversion of triacetin was between one and four minutes.Thereafter, the amount of PAA in solution is reduced because itundergoes high pH degradation slowly over the following 10 minutes.

Example 13

FIG. 1 is a schematic representation of an example of a system 10 thatwas used to perform an embodiment of one of the methods described aboveto prepare a non-equilibrium solution of PAA on a site having apoint-of-use. Triacetin was used as the acetyl precursor and 50% sodiumhydroxide was used as the aqueous source of an alkali metal hydroxide.

A container 120 of a hydrogen peroxide-acetyl precursor solution, whichwas a hydrogen peroxide-triacetin solution, and a container 140 of 50%sodium hydroxide were each equipped with chemical delivery diaphragmpumps 115 and 135, respectively. Inlet water 90, which was softened, wasprovided from a water source on the site having the point-of-use. Inletwater 90 was directed through a pressure regulator 100 and flow meter105, then into a section of pipe where the hydrogen peroxide-triacetinsolution was introduced through injection quill 110. Mixing wasaccomplished using static mixer 125. Then, the sodium hydroxide solutionwas added through injection quill 130 to form a reaction medium.

The hydrogen peroxide-triacetin solution and the sodium hydroxidesolution may be added in a sequential manner as described, where thehydrogen peroxide-triacetin solution was added first, or they may beadded to the water simultaneously through a “T” fitting placed beforestatic mixer 125. If a T fitting is used, the hydrogenperoxide-triacetin solution and the 50% sodium hydroxide solution areintroduced to opposite ends of the T fitting and the mixture is injectedinto the pipe of water. In other embodiments, the hydrogen peroxide andtriacetin may be added separately, or sequentially, with either onefirst, or simultaneously, with the sodium hydroxide added eithersimultaneously with, or after, the hydrogen peroxide and triacetin.

The reaction medium was introduced to a residence chamber 145 whichprovided reaction time and contained a packing material to promotemixing. Residence chamber 145 was designed to be of a volume such thatat a total flow rate of one gallon per minute, by the time the reactionmedium reached sampling port 160, 30 seconds had elapsed since thesodium hydroxide solution had been added. A pH probe 155 monitored thepH of the mixture.

A controller 150 was interfaced to the flow meter 105 of the inlet water90, and also to the chemical delivery diaphragm pumps 115 and 135. Thecontroller 150 monitored the rate of die inlet water 90 and governed therate at which the hydrogen peroxide-triacetin solution and the NaOHsolution were introduced. If the flow of inlet water 90 decreasedbecause of lower PAA requirements at the point-of-use 195, the rates atwhich the hydrogen peroxide-triacetin solution and the NaOH solutionwere pumped decreased accordingly. If the flow of inlet water 90increased because of higher PAA requirements at the point-of-use 195,the rates at which the hydrogen peroxide-triacetin solution and the NaOHsolution were pumped increased accordingly. If the flow of inlet water90 stopped, pumps 115 and 135 stopped. Thus, the generation of PAA wasboth continuous and intermittent, and was tailored to the PAArequirements at the point-of-use.

The rate of the reaction between the hydrogen peroxide and the triacetinto form PAA is dependent upon the temperature of inlet water 90. If thetemperature of inlet water 90 is high (for example, about 70° F.), themaximum conversion of triacetin into PAA may occur after 30 seconds, inwhich case the entire reaction medium was directed to the point-of-use195. However, if the temperature of inlet water 90 is low (for example,about 32° F.), longer reaction times may be necessary to maximize theconversion of triacetin into PAA. Then, the reaction medium was directedthrough one or more residence chambers 165, 175, and 185 which alsocontained a packing material to promote turbulence and cause thoroughmixing. Residence chambers 165, 175, and 185 were designed to be ofvolumes such that at a total flow rate of one gallon per minute, thereaction medium reached sampling port 170 in one minute, sampling port180 in two minutes, and sampling port 190 in five minutes, to permitsampling at different time intervals.

Thus, depending on the temperature of the inlet water, the time toachieve the maximum conversion of hydrogen peroxide and triacetin intoPAA was determined by sampling and analyzing the solution at sampleports 160, 170, 180, and 190. The entire flow was then directed from thesampling port with the highest amount of PAA to the point-of-use 195. Inpractice, the PAA generated from the reaction of hydrogen peroxide withtriacetin is typically diluted at the point-of-use 195.

Point-of-use 195 may be recirculating cooling water; municipalwastewater; poultry chill tank water; water used to sanitize meat,poultry, or seafood products; fruit aid vegetable rinse water; or waterused to clean and sanitize equipment used in the dairy, food, orbeverage processing industries.

Example 14

Referring again to FIG. 1, a 55-gallon drum container 120 of a hydrogenperoxide-triacetin solution was prepared by mixing triacetin (251.5 lbs)with 50% hydrogen peroxide (298.4 lbs). The resulting 550 lbs ofhydrogen peroxide-triacetin solution had a specific gravity of 1.19 g/mL(10 lbs/gal) and contained 54.3% hydrogen, peroxide and 45.7% triacetin.Thus, the mole ratio of hydrogen peroxide:triacetin was 3.8:1. Theapparatus depicted in FIG. 1 was used to continuously and intermittentlyprepare an approximately 1% PAA solution.

Softened Local city water was directed through pressure regulator 100 ata flow rate of one gallon per minute as measured by flow meter 105. Thecontainer 120 of hydrogen peroxide-triacetin solution was equipped witha draw down tube so that the flow rate of the mixture could be measured.Diaphragm pump 115 injected the hydrogen peroxide-triacetin solutionthrough injection quill 110. The hydrogen peroxide-triacetin solutionwas then mixed with the softened water using static mixer 125. Acontainer 140 of 50% NaOH was also equipped with a draw down tube tomeasure the flow pumped by diaphragm pump 135 into injection quill 130.

The percent of PAA generated was measured by quenching samples drawnthrough the sampling ports in mineral acid, followed by use of the cericsulfate-iodometric titration method. Table XVII summarizes the resultsof several trials where it was sought to maximize the conversion oftriacetin into PAA and minimize the amount of 50% NaOH used.

TABLE XVII % Triacetin Hydrogen Peroxide- Sample % PAA ConvertedTriacetin Mix Flow NaOH Flow pH (PAA Trial # Port Generated to PAA Rate(mL/min) Rate (mL/min) solution) 1 160 1.083 65.42 115.73 112.11 ~13 2170 1.073 64.82 115.73 112.11 13.19 3 160 0.955 57.32 116.79 122.1213.37 4 160 1.058 63.39 116.79 114.93 13.11 5 160 1.061 63.3 116.79 98.112.9 6 160 1.102 68.96 110.82 85.01 12.91 7 170 1.055 55.59 132.64 99.7712.95 8 160 0.978 59.91 115.5 74 12.62 9 180 0.936 56.7 114.25 78 12.64

It can be seen that, the amount of PAA generated, and hence theconversion of triacetin into PAA, increased with the increasing flowrate of NaOH. For this mole ratio of hydrogen peroxide:triacetin of3.8:1, the maximum amount of PAA was generated between 30 seconds(sample port 160) and two minutes (sample port 180) from the time theNaOH was added at injection quill 130. The flow rate of 74-78 mL/min of50% NaOH was the optimum flow rate as it resulted in an efficientutilization of triacetin converted into PAA, consumed only a moderateamount of 50% NaOH, and had a lower pH that would have less impact onthe pH of the receiving water.

Example 15

E. coli O157:H7 bacteria (ATCC 35150) was cultured in nutrient broth(Sigma, St. Louis, Mo.) by incubation for two days at 35° C. Thebacteria were separated from the nutrient broth by centrifugation andcarefully resuspended in two liters of sterile phosphate buffer, whichwas then split into two one-liter test solutions.

Salmonella typhimurium bacteria (ATCC 14028) was cultured in nutrientbroth (Sigma, St Louis, Mo.) by incubation, for two days at 35° C. Thebacteria were separated from the nutrient broth by centrifugation andcarefully resuspended in two liters of sterile phosphate buffer, whichwas then split into two one-liter test solutions.

The amount of E. coli O157:H7 and Salmonella typhimurium bacteria weremeasured by serial dilution and plating on 3M E. coli plates and 3MEnterobacteriaceae Petrifilms, respectively.

A 1000 ppm stock of PAA was made by weighing 0.6386 g of Perasan MP-2(5.83% hydrogen peroxide and 15.66% PAA) and adding water up to 100 g.Perasan MP-2 is an equilibrium product of PAA (Enviro Tech ChemicalServices, Inc., Modesto, Calif.). Side-by-side, one of the E. coli andone of the Salmonella test solutions were treated with a nominal dose of1.0 ppm PAA by adding one mL of the 1000 ppm PAA stock solution to eachsample. After one minute, approximately 100 mL of each test solution wasremoved, and sodium thiosulfate (0.5 g) was added to neutralize the PAAand hydrogen peroxide oxidants. After five minutes, sodium thiosulfate(0.5 g) was added to the remaining test solution to neutralize the PAAand hydrogen peroxide in the rest of the test solutions. The amount ofviable E. coli O157:H7 and Salmonella typhimurium bacteria remaining inthe test solutions at the one-minute and five-minute contact times weremeasured by serial dilution and plating on 3M E. coli Petrifilms and 3MEnterobacteriaceae, respectively.

A 1% solution of PAA was prepared by combining 30.90 g of a mixture of50% hydrogen peroxide and triacetin (54.22% hydrogen peroxide and 45.78%triacetin) with 929.4 g of water, and then adding 50% NaOH (40.53 g).The PAA solution had a pH of 12.79. The mole ratio of this mixture was3.8:7.8:1 NaOH:hydrogen peroxide:triacetin. One minute afterpreparation, the second one-liter E. coli solution and the secondone-liter Salmonella solution were treated with a nominal dose of 1.0ppm PAA by adding 0.10 g of the 1% PAA solution to each sample. The testsolution contact times, neutralization, and plating procedures werereplicated for those that employed PAA from Perasan MP-2.

All 3M E. coli Petrifilms and 3M Enterobacteriaceae Petrifilms wereincubated at 35° C. for 24 hours. After incubation, the plates wereenumerated.

Table XVIII shows the microbiological results of the E. coli O157:H7test solutions before treatment with PAA, one minute after the sampleswere dosed with a nominal 1.0 ppm PAA, and five minutes after beingdosed with PAA. The E. coli test solution started with log₁₀ 6.99 CFU/mLprior to being treated with 1.0 ppm of PAA from Perasan MP-2 or with 1ppm of PAA from the 1% PAA solution.

The E. coli test solution treated with 1.0 ppm PAA from Perasan MP-2contained a log₁₀ 6.74 CFU/mL after one minute. This corresponds to43.48% reduction. After five minutes, log₁₀ 6.34 CFU/mL remained (77.50%reduction). The E. coli solution treated with a nominal 1.0 ppm PAA fromthe 1% PAA solution contained a log₁₀ 6.78 CFU/mL after one minute and6.63 CFU/mL alter five minutes, respectively, corresponding to 38.02%and 56.12% reductions, respectively.

TABLE XVIII E. coli O157:H7 log₁₀ CFU/ml log₁₀ % Description remainingreduction reduction Control 6.99 N/A N/A Perasan MP-2 (1 min) 6.74 0.2543.48 Perasan MP-2 (5 min) 6.34 0.65 77.50 1% PAA solution (1 min) 6.780.21 38.02 1% PAA solution (5 min) 6.63 0.36 56.12

Table XIX shows the microbiological results of the Salmonellatyphimurium test solutions before treatment with PAA, one minute afterthe samples were dosed with a nominal 1.0 ppm PAA, and five minutesafter being dosed with PAA. The Salmonella test solution started withlog₁₀ 7.07 CFU/mL prior to being treated with PAA from Perasan MP-2 orwith the 1% PAA solution.

The Salmonella solution treated with a nominal 1.0 ppm PAA from PerasanMP-2 contained a log₁₀ 1.76 CFU/mL after one minute and 0.70 CFU/mLafter five minutes, corresponding to >99.999% reduction at both contacttimes. The Salmonella test solution treated with 1.0 ppm PAA from the 1%PAA solution contained a log₁₀ 6.69 CFU/mL after one minute. Thiscorresponds to 58.31% reduction. After five minutes, log₁₀ 4.95 CFU/mLremained (99.24% reduction).

TABLE XIX Salmonella typhimurium log₁₀ CFU/ml log₁₀ % Descriptionremaining reduction reduction Control 7.07 N/A N/A Perasan MP-2 (1 min)1.76 5.31 99.9995 Perasan MP-2 (5 min) 0.70 6.37 >99.9999 1% PAAsolution (1 min) 6.69 0.38 58.31 1% PAA solution (5 min) 4.95 2.12 99.24

The data in tables XVIII and XIX demonstrate that the 1% PAA hadantimicrobial efficacy. After five minutes, the efficacy of this PAA was99.24%, about equal to that of the Perasan MP-2, which was >99.9999%.The difference in efficacy at one minute was likely not of statisticalsignificance, given that the comparison was only at the one-minuteinterval

5. Solid Compositions for Bleaching and Stain Removal

A freely-flowable, solid peroxygen bleaching and stain removalcomposition comprises a liquid acetyl precursor, a water-soluble solidsource of hydrogen peroxide, and a water-soluble solid source ofalkalinity. A preferable liquid acetyl precursor is triacetin. The watersoluble solid source of hydrogen peroxide is preferably sodiumpercarbonate, although sodium perborate monohydrate or sodium perboratetetrahydrate may be used. The water-soluble solid source of alkalinityacts as a pH control agent, and may be an alkali metal or earth alkalimetal bicarbonate, carbonate, sesquicarbonate, borate, silicate, orhydroxide. Examples include sodium bicarbonate, sodium carbonate, sodiumsesquicarbonate, sodium borate, sodium borate decahydrate (borax),sodium metasilicate, and sodium hydroxide.

In an embodiment, the composition comprises about 0.99% to about 8.45%triacetin, about 13% to about 54% sodium percarbonate, and about 24% toabout 44% solid source of alkalinity.

The composition may optionally contain other components to improveperformance. These components may prevent soil redeposition, sequesterwater hardness, increase dispercency, and lower surface tension.

Metal ions present in the bleaching medium can have a tendency todeposit on the substrates being bleached. Therefore, the solid bleachingcomposition may optionally contain a metal chelating agent such as apolyacrylate, a phosphonate, a maleic acid, a salt ofethylenediaminetetraacetic acid, a salt of nitrilotriacetic acid, or asalt of gluconic acid.

Surfactants reduce the surface tension of the bleaching medium andenhance the process of cleaning the soiled article. Surfactants alsodisperse the soil particles removed from the article and keep themsuspended. Therefore, the solid bleaching composition may optionallycontain a surfactant, such as an anionic, cationic, amphoteric, ornon-ionic surfactant.

The solid bleaching composition may also optionally contain a solidzeolite, such as sodium zeolite, which acts to capture calcium andmagnesium ions that may be present in the bleaching medium that wouldotherwise interact with an anionic surfactant, causing the surfactant toprecipitate and removing it from the bleaching medium.

The composition may also optionally contain an inert, solid filler, suchas anhydrous sodium sulfate, sodium, sulfate decahydrate, or sodiumchloride. The filler increases the total ionic strength of the aqueousphase, but imparts no chemical properties to the bleaching medium.

To make the solid peroxygen bleaching and stain removal composition, thewater soluble solid source of hydrogen peroxide, the water-soluble solidsource of alkalinity, any chelating agent, any sufactant, and any fillerare blended with the liquid triacetin to form a solid bleachingcomposition. The components may be added in any order. Any blendingequipment may be used. Suitable examples of equipment include a ribbonand paddle blender, a V and double-cone blender, a Nauta screw mixer,and a rotating cement mixer. Alternatively, the ingredients may beblended by milling using a pulveriser mill, a ball mill, a hammer mill,a pin mill, an air mill, or a roller mill. Blending is performed forsufficient time to create a homongenous mixture. The mixture is afreely-flowable solid which is readily discharged from the blender.

Example 16

A series of tests were performed to determine whether triacetin, aliquid at room temperature, could be blended with a solid source ofhydrogen peroxide to form a solid bleaching and stain removalcomposition that did not clump or turn into a sticky, non-flowable mass.The components listed in Table XX were mixed together to form a solidperoxygen bleach precursor.

TABLE XX Component % Sodium carbonate, anhydrous 26.3 Sodiumpercarbonate 58.9 Sodium sulfate decahydrate 13.8 Surfactant (60% sodiumdodecylbenzene sulfonate) 1.0 Total 100

This solid peroxygen bleach precursor was then blended withincrementally increasing amounts of liquid triacetin. At each addition,the product was examined for flowability and for the odor of PAA. TableXXI summarizes the findings when up to 9.1 g of liquid triacetin wasblended into 100 g of the solid peroxygen bleach precursor set forthabove.

TABLE XXI Wt. of triacetin added to solid peroxygen Freely-flowablesolid or Odor of bleach precursor (g) sticky and clumping PAA 1 Freely-flowable solid None 2 Freely- flowable solid None 3 Freely- flowablesolid None 4 Freely- flowable solid None 5 Freely- flowable solid None 6Freely- flowable solid None 7 Freely- flowable solid None 8 Freely-flowable solid None 8.45 Freely-flowable solid None 9 Sticky andclumping None 9.1 Sticky and clumping None

Surprisingly, even though triacetin is a liquid, the solid peroxygenbleach precursor (100 g) could be blended with up to 8.45 g of thetriacetin to form a freely-flowable solid composition, without becominga sticky, non-flowable product which would not pour easily or wouldbecome a solid mass upon storage inside a container.

The solid peroxygen bleaching and stain removal composition wascalculated to contain the following percentage of components, listed inTable XXII.

TABLE XXII Component % Sodium carbonate, anhydrous 24.14 Sodiumpercarbonate 53.90 Sodium sulfate decahydrate 12.56 Surfactant (90%sodium dodecylbenzene sulfonate) 0.95 Triacetin 8.45 Total 100

Another unexpected result was that after storing the composition forover one year at ambient temperature, the composition still had notdeveloped an odor of PAA.

These surprising results are in contest to the current belief that aliquid acetyl precursor, such as triacetin, could not be utilized with asolid source of hydrogen peroxide in a non-chlorine peroxygen bleachingand stain removal composition, for at least two reasons. First when anon-chlorine peroxygen bleaching composition is used in residential andcommercial laundering applications, the product must be afreely-flowable solid. Typically, the acetyl precursor in anon-chlorinated peroxygen bleach is present in amounts up to 10%. It wasbelieved that blending a liquid at this level with the other drycomponents of the laundry bleach would create a sticky, clumping mass,rather than, a freely-flowable solid, and would therefore not beacceptable to the user. Second, it was assumed that a liquid acetylprecursor would interact with the solid source of hydrogen peroxide andany free water or water of crystallization associated with othercomponents, and thus form PAA in the product during storage, beforebeing introduced to the aqueous bleaching medium. The high volatilityand strong odor of the PAA would be unacceptable to the user of such aproduct.

Example 17

Two solid peroxygen bleaching and stain removal compositions wereprepared with the components listed in Table XXIII.

TABLE XXIII % Charge Weights, g Components of Composition A Premix 1Sodium Percarbonate 13 195 NANSA HS 90 1.5 22.5 Sodium Metasilicate(Anhydrous) 19.5 292.5 Sodium Sulfate (Anhydrous) 41 615 Triacetin 4 60Premix 2 Mineral Oil 1 15 Sodium Hydroxide Beads 4 60 Soda Ash 16 240Components of Composition B Premix 1 Sodium Percarbonate 13 195 NANSA HS90 1.5 22.5 Sodium Metasilicate (Anhydrous) 19.5 292.5 Sodium Sulfate(Anhydrous) 43 645 Triacetin 4 60 Premix 2 Mineral Oil 1 15 SodiumHydroxide Beads 2 30 Soda Ash 16 240

In both cases, Premix 1 was prepared by kneading the NANSA HS 90 (asodium dodecylbenzenesulfonate surfactant) with the sodium sulfate. Thesodium sulfate helped break up the sticky surfactant efficiently. Then,the sodium percarbonate, the sodium metasilicate, and the triacetin wereadded and mixed by hand.

In both, cases. Premix 2 was prepared by mixing the sodium hydroxidebeads with the mineral oil to afford a well-coated mixture, with somefree-standing mineral oil remaining. Soda ash was blended in portions totake up the excess liquid and to provide a free-flowing solid mixture.

Premix 2 was blended in portions into Premix 1, and the final solidcomposition was mixed well by hand.

Both compositions A and B, which were held in uncovered bowls at ambienttemperature after preparation, exhibited slow weight gain over time,most likely due to absorbance of water from the air. Each compositionhad gained 2.4% of its initial weight over a period of three days.

Neither composition exhibited significant exothermic behavior. However,composition A was hotter at the end of preparation and cooled moreslowly than composition B. The temperature of composition A was 85° F.immediately after preparation, rose to 88° F. over the next ten minutes,and then fell slowly to 74° F. The temperature of composition B was 80°F. immediately after preparation, rose to 81° F. over the next twentyminutes, and then fell slowly to 65° F.

The solid peroxygen bleaching and stain removal composition describedabove may be used as follows.

First, the solid peroxygen, composition is introduced to an aqueousmedium that is used for bleaching or stain removal of at least onearticle contained within the aqueous medium. For bleaching of laundryarticles, about 5 g of bleaching composition is introduced for everyliter of water used in the bleaching cycle. For home use, the bleachingcomposition can be added manually at the start of the wash. Forcommercial laundry systems, the bleaching composition may be introducedjust before the bleaching cycle, toward the end of the wash andfollowing the soil removal cycle. In most commercial and residentiallaundry machines, bleaching cycles are typically about 10-15 minutes.

Second, the composition is allowed to dissolve and react to form thebleaching medium containing PAA. The solid source of hydrogen peroxide,such as sodium percarbonate, and the solid source of alkalinity, such assodium hydroxide, dissolve in the laundry water and cause the pH of thewater to increase to above about 10.5.

While not wishing, to be bound by theory, it is believed that underelevated pH conditions, hydrogen peroxide dissociates according to thefollowing equation:H₂O₂=H⁺HO₂ ⁻

The perhydroxyl anion (HO₂ ⁻) then effects nucleophilic substitutionreactions on the carbonyl groups of triacetin, in a perhydrolysisreaction, to form PAA and 1,2,3-propanetriol (glycerine). The laundrywater would also contain unreacted hydrogen peroxide, unreactedtriacetin, and sodium hydroxide.

Third, the aqueous solution of PAA and the unreacted hydrogen peroxideare mixed for sufficient time to effect bleaching or stain removal ofthe articles contained within the aqueous medium. Both commercial andresidential bleaching cycles are about 10-15 minutes.

Fourth, the article is rinsed with fresh water so that it becomessubstantially free of PAA and the unreacted hydrogen peroxide, theglycerine, the unreacted triacetin, and the sodium hydroxide. Generally,for a laundered article, the washing machine is programmed to empty thebleaching medium and replace it with fresh water. The machine canagitate the articles with the rinse water to enhance the rinsingprocess.

Fifth the article is allowed to dry. Any suitable means of drying thebleached articles may be employed. This includes the use of centrifugalforces to mechanically dewater the articles prior to introducing the wetarticles to another machine before the articles are tumbled in a streamof hot air. Alternatively, the articles may be allowed to air drywithout the use of externally-applied heat.

Example 18

Laundry swatches were made by cutting a tea towel into 50 equal 5×4 inchsheets. They were then separated into seven groups of seven swatches.Six of the groups were stained and the seventh group was left unstainedfor comparison purposes. Five of the groups that were stained werestained by soaking them in one of the following: black tea, black,coffee, red wine, blood (park), and acetone-extracted chlorophyll. Thesixth group of swatches was stained by rubbing them on green grass.After allowing the stained swatches to dry, and before challenging thestains, the swatches were set aside for two months to allow the stainsto set in the fabric.

A solid peroxygen bleaching and stain removal composition (200 g) wasprepared by blending sodium percarbonate (104.0 g), triacetin (8.00 g),soda ash (80.01 g), and sodium, hydroxide beads (8.00 g). The finalproduct was a freely-flowable solid.

The composition was tested using 1:100 dilution at both 75° F. and 104°F. The initial pH was measured and the concentrations of PAA andhydrogen peroxide were evaluated using the method of U.S. Pat. No.7,651,724. At each temperature, the composition (1.0 g) was weighed outinto a glass beaker (100 mL). To the beaker, city water (99 mL) wasadded while mixing on a stir plate. The pH and PAA generation profilewas then monitored over the next 10-13 minutes to model the times of atypical low temperature and high temperature bleaching cycle. For citywater at 75° F., the initial pH measured 11.2 and the PAA measuredhighest at 10.5 minutes (123 ppm PAA and 1594 ppm hydrogen peroxide).The test with city water at 104° F. had the same initial pH of 11.2, butthe PAA measured highest at 5.5 minutes (133 ppm PAA and 1494 ppm H₂O₂).Table XXIV shows the amount of PAA generated and the amount of hydrogenperoxide remaining over time at 75° F. at a pH of 11.2. Table XXV showsthe amount of PAA generated and the amount of hydrogen peroxideremaining over time at 104° F. at a pH of 11.2.

TABLE XXIV Time (min) ppm PAA ppm Hydrogen Peroxide 1 61 1717 3 106 16735.2 113 1694 7.3 121 1571 10.5 123 1594 13.5 120 1547

TABLE XXV Time (min) ppm PAA ppm Hydrogen Peroxide 0.5 72 1569 2.8 1251426 5.5 133 1494 7.8 122 1427 10.3 119 1405

The stain removal ability of the composition was determined by comparingtreated swatches to control swatches (swatches washed in just city waterfor the same amount of time and at elevated temperature) and non-stainedswatches. The description of the swatches is set forth in Table XXVI.Three stained swatches were used for each test. The composition (10.0 g)was weighed, into a beaker (2000 mL). To this beaker a measured amountof hard water (990.0 g) was added at ambient temperature (64° F.). Theswatches were added, to the solution and agitated by mixing with aplastic utensil for 10 minutes to simulate a laundry bleaching cycle.After 10 minutes, the wash water was discarded and a water rinse wasperformed by adding fresh city water (1000.0 g) to the swatches andagitating for two minutes using the same plastic utensil. The swatcheswere immediately removed thorn the beaker after rinsing, wrung out byhand, and laid to dry. These steps were then repeated using water at anelevated temperature (120° F.).

A control swatch was obtained by taking one swatch at a time from eachstain group and washing in city water at an elevated temperature (120°F.) for 10 minutes in the same manner as the treated swatches. After thewash, the swatches were immediately removed, wrung out by hand, and laidto dry.

TABLE XXVI Type of Swatches Description Treated Swatches Swatchessubjected to bleaching for 10 minutes using bleaching formulation withtriacetin and a 2-minute rinse with hard water Control Swatches Swatchessubjected to only an elevated temperature (120° F.) hard water wash for10 minutes Non-Stained Non-altered swatches Swatches

The bleaching ability of the test swatches was obtained by visualcomparison of the treated swatches to the control swatches (treated withwater only) and the non-stained swatches. The scale of bleaching abilityof the composition was rated on a scale of 0 to 10, with 0 representingno apparent bleaching or stain removal properties of the swatchescompared to the control and 10 representing bleaching of swatches to theoriginal color (i.e., identical to the non-stained swatches). Threeindividuals rated, the bleaching ability of the triacetin-containingformulation on the swatches independently. The average ratings from thethree individuals are shown in Table XXVII.

TABLE XXVII Bleaching Formula Bleaching Formula Type of Stain at 64° F.at 120° F. Black Tea 5 8 Black Coffee 2 8 Red Wine 3 7 Blood (pork) 3 3Extracted chlorophyll 0 0 Grass Stains 0 1

it can be seen that, in general, the composition displayed enhancedstain removal properties at elevated temperature. Excellent stainremoval, properties were obtained for black tea and black coffee, andmore moderate performance with red wine and blood. The composition hadvirtually no effect on grass stains or the chlorophyll pigment that wasacetone-extracted from green grass.

The invention has been described above with the reference to thepreferred embodiments. Those skilled in the art may envision otherembodiments and variations of the invention that fall within the scopeof the claims.

We claim:
 1. A method of generating a non-equilibrium solution of peracetic acid, comprising: a. providing water; b. introducing triacetin and aqueous hydrogen peroxide to the water; c. mixing the triacetin and the aqueous hydrogen peroxide with the water to form a mixture; d. adding an aqueous source of an alkali metal or earth alkali metal hydroxide to the mixture; and e. forming a reaction medium comprising a non-equilibrium solution of peracetic acid.
 2. The method of claim 1, wherein the triacetin and the aqueous hydrogen peroxide are introduced simultaneously.
 3. The method of claim 1, wherein the triacetin and the aqueous hydrogen peroxide are introduced sequentially with either one first.
 4. The method of claim 1, wherein the provided water is an aqueous stream.
 5. The method of claim 1, wherein the provided water is contained in a mixing tank or other vessel.
 6. The method of claim 1, wherein the aqueous source of the alkali metal or earth alkali metal hydroxide is sodium hydroxide.
 7. The method of claim 6, wherein, the sodium hydroxide is about 1.82% to about 7.28%.
 8. The method of claim 1, wherein step (d) is performed simultaneously with step (b).
 9. The method of claim 1, further comprising allowing the reaction medium sufficient time to maximize the conversion of the hydrogen peroxide and the triacetin into peracetic acid.
 10. The method of claim 9, wherein the time to maximize the conversion of the hydrogen peroxide and the triacetin into peracetic acid is about 30 seconds to about five minutes.
 11. The method of claim 10, wherein the percent of triacetin that is converted into peracetic acid is about 40.9% to about 85.7%.
 12. The method of claim 6, wherein the mole ratio of the sodium hydroxide to the hydrogen peroxide to the triacetin is about 4.2:3.8:1.
 13. The method of claim 1, wherein said steps (a) through (e) are performed on a continuous basis.
 14. The method of claim 1, wherein said steps (a) through (e) are performed on an intermittent basis. 